Airplanes have utilized various emergency power units (“EPUs”) to provide electrical power in the event of an engine failure. However, existing emergency power units encounter operational challenges. For example, ram air turbines can be damaged during deployment into the aircraft's slipstream. Also, compressor bleed air driven systems are inoperable if the main engine fails unless there is a low-pressure spool generator operating during wind milling of the main engine fan(s), though this spool generator adds unwanted weight and complexity. Moreover, solid propellant-based power systems are unstable and prone to contamination and aging, and extant fuel cell based emergency power units require near-atmospheric inlet air pressure and relatively high inlet temperatures. Thus, there is a need for an advanced integrated hybrid EPU that overcomes these challenges while providing reliable onboard emergency electrical power.